FIG. 1 shows an electronic circuit CI suitable for a contactless application including a diode bridge DBr (typically a Graetz bridge) for delivering a direct current voltage VDC from the voltage present at the terminals ACo and AC1 of the antenna ANT1 of the circuit, coupled to the antenna ANT2 of a reader RD.
In this application, the circuit CI includes a latch circuit LTC, conventionally having four transistors T2-T5, adapted to store a digital data element. A reset transistor T1 is also shown, and is controlled by a signal TX delivered by the circuit's processing means COM.
The latch LTC is formed in a box structure N-ISO, itself formed in a semiconductor substrate PSUB. The transistors T1-T3 are formed in a box structure PW, itself formed in the box structure N-ISO. The interfaces between the differently doped box structures form diodes Dpwniso and Dnisopsub.
A current flows in the antenna ANT1 in a direction representative of the data element stored in the latch LTC, so that this element can be read by the reader RD.
The diodes of the bridge DBr, based on polycrystalline silicon, also called polysilicon, are usually formed directly in the substrate PSUB, or in the box structure N-ISO, and this may introduce undesirable bipolar effects.
In fact, recurrent problems have been encountered in the use of diodes whose doped regions are directly implanted in the substrate. These undesirable effects are, for example, due to parasitic PN junctions, and are usually seen in the starting or latching of the circuit.
It is desirable to avoid these parasitic effects in a way which is simple and compatible with non-volatile memory technology.
On the other hand, some dopant diffusion processes in the usual diode manufacturing methods are poorly controlled, for example because of masks requiring strict alignment which is difficult to establish, the defects in this alignment resulting in unpredictability of the characteristics of the diodes.